1. Field of the Invention
The invention is related to the field of packet communication systems, and in particular, to timing recovery in a packet network using a buffer.
2. Description of the Prior Art
Packet networks include many packet devices that communicate with each other. The packet devices communicate according to a standardized protocol, such as TCP/IP, which transfers data in the form of packets. The packets are transmitted as an electrical signal, an optical signal, a wireless signal, etc., depending on the transport medium between the packet devices. Packet devices in the packet network should be substantially synchronized in order for the packet devices to communicate reliably. For instance, when streaming data is sent over the packet network, the stream of data needs to be played out of the network at the receiving end at the same rate the stream of data was sent into the network at the transmitting end. If this synchronization is not established, the slower end will be overrun with data it must discard and the faster end will become starved for data.
Network operators could synchronize internal clocks of the packet devices by installing very-accurate clocks in each of the packet devices. The accurate clocks do not drift very far from the base, reference frequency from which they are configured to operate. Unfortunately, the accurate clocks are expensive and they increase the total cost of the packet network. Expensive clocks would be impractical to use in wide spread residential packet devices.
The network operators could also synchronize the internal clocks by transmitting a universal clock signal to the packet devices over a physical transport medium. The universal clock signal could come from a universal clock used throughout the packet network. Packet devices in the packet network can recover the universal clock signal from the transport medium. For instance, a packet device can detect and filter out a clock pulse from an electric signal on a copper wire. Recovering a clock signal from a transport medium is well known to those skilled in the art. Unfortunately, the accuracy of the recovered clock signal depends on the quality of the transport medium used to carry the clock signal. Packet devices may not be able to recover an accurate clock signal from a low quality transport medium. For instance, a T1 line may carry a high quality clock signal whereas another type of line may not carry a quality clock signal.